SpringCloud 第三篇: 服務消費者(Ribbon / Feign)
前面的文章學習了服務的註冊和發現。在微服務架構中,業務都會被拆分成一個獨立的服務,服務與服務的通訊是基於http restful的。Spring cloud有兩種服務呼叫方式,一種是ribbon+restTemplate,另一種是feign。在這一篇文章要學習的是如何 通過 rest + ribbon 和 Feign 來消費服務,也就是跨服務呼叫。
1. Rest + Ribbon
1.1 Ribbon 簡介
ribbon 是一個客戶端負載均衡器,可以簡單的理解成類似於 nginx的負載均衡模組的功能,可以很好的控制http和tcp的一些行為。
1.2 建立服務消費者
在之前那個專案裡面建立一個Module,和之前建立服務相似的過程,注意下要匯入Ribbon所需的包。
建立完成之後的 pom.xml 內容如下:
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.example</groupId> <artifactId>demo</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> <name>demoRibbon</name> <description>Demo project for Spring Boot</description> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.0.2.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> <java.version>1.8</java.version> <spring-cloud.version>Finchley.BUILD-SNAPSHOT</spring-cloud.version> </properties> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId> </dependency> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-netflix-ribbon</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> </dependencies> <dependencyManagement> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-dependencies</artifactId> <version>${spring-cloud.version}</version> <type>pom</type> <scope>import</scope> </dependency> </dependencies> </dependencyManagement> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> <repositories> <repository> <id>spring-snapshots</id> <name>Spring Snapshots</name> <url>https://repo.spring.io/snapshot</url> <snapshots> <enabled>true</enabled> </snapshots> </repository> <repository> <id>spring-milestones</id> <name>Spring Milestones</name> <url>https://repo.spring.io/milestone</url> <snapshots> <enabled>false</enabled> </snapshots> </repository> </repositories> </project>
1.3 添加註解
在服務的啟動類中,通過 @EnableDiscoveryClient 指向服務中心註冊,並且向程式的 ioc 注入一個bean: restTemplate;並通過@LoadBalanced註解表明這個restRemplate開啟負載均衡的功能。
package com.example.demo; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.cloud.client.loadbalancer.LoadBalanced; import org.springframework.cloud.netflix.eureka.EnableEurekaClient; import org.springframework.context.annotation.Bean; import org.springframework.web.client.RestTemplate; @SpringBootApplication @EnableEurekaClient public class DemoRibbonApplication { public static void main(String[] args) { SpringApplication.run(DemoRibbonApplication.class, args); } @Bean @LoadBalanced RestTemplate restTemplate(){ return new RestTemplate(); } }
1.4 配置資訊
eureka:
client:
serviceUrl:
defaultZone: http://localhost:10000/eureka/
server:
port: 10001
spring:
application:
name: service-demo
1.5 測試
寫一個測試類HelloController,通過之前注入ioc容器的restTemplate來消費service-demo服務的“/hello”介面,在這裡我們直接用的服務名替代了具體的url地址,在ribbon中它會根據服務名來選擇具體的服務例項,根據服務例項在請求的時候會用具體的url替換掉服務名,如果服務名帶有下劃線都無法呼叫成功,程式碼如下:
package com.example.demo.controller;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.client.RestTemplate;
@RestController
public class HelloController {
@Autowired
RestTemplate restTemplate;
@RequestMapping("/wlecome")
public String wlecome(@RequestParam String name){
String wlecome = restTemplate.getForObject("http://SERVICE-DEMO/hello?name="+name, String.class);
return wlecome;
}
}
由於我們程式碼輸出的是的service-demo服務的埠號,所以 prot 顯示的是10001。
這說明當我們通過呼叫 restTemplate.getForObject("http://SERVICE-DEMO/hello?name="+name, String.class) 方法時,已經做了負載均衡,訪問了不同的埠的服務例項。
2. Feign
2.1 Feign簡介
官網裡面解釋:Feign是一個宣告式的偽Http客戶端,它使得寫Http客戶端變得更簡單。使用Feign,只需要建立一個介面並註解。它具有可插拔的註解特性,可使用Feign 註解和JAX-RS註解。Feign支援可插拔的編碼器和解碼器。Feign預設集成了Ribbon,並和Eureka結合,預設實現了負載均衡的效果。
總結就是:
1. Feign 採用的是基於介面的註解;
2. Feign 可以和其他的開源工具整合工作;
3. Feign 整合了ribbon。
2.2 建立消費者服務
建立一個Module,和之前建立服務相似的過程,注意下要匯入Feign所需的包。
建立完成之後的 pom.xml 內容如下:
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.example</groupId>
<artifactId>demo</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>demoFeign</name>
<description>Demo project for Spring Boot</description>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.2.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
<spring-cloud.version>Finchley.BUILD-SNAPSHOT</spring-cloud.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>${spring-cloud.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
<repositories>
<repository>
<id>spring-snapshots</id>
<name>Spring Snapshots</name>
<url>https://repo.spring.io/snapshot</url>
<snapshots>
<enabled>true</enabled>
</snapshots>
</repository>
<repository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
</repositories>
</project>
2.3 添加註解
在服務的啟動類中,通過@EnableDiscoveryClient向服務中心註冊,加上@EnableFeignClients註解開啟Feign的功能:
package com.example.feign;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.openfeign.EnableFeignClients;
@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
public class DemoFeignApplication {
public static void main(String[] args) {
SpringApplication.run(DemoFeignApplication.class, args);
}
}
2.4 配置資訊
eureka:
client:
serviceUrl:
defaultZone: http://localhost:10000/eureka/
server:
port: 10004
spring:
application:
name: service-feign
2.5 測試
定義一個feign介面,通過@FeignClient(“服務名”),來指定呼叫哪個服務,需要注意的是如果呼叫的服務名帶有下劃線在啟動時會報錯。比如在程式碼中呼叫了service-demo服務的“/hello”介面,程式碼如下:
package com.example.feign.feign;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
@FeignClient("service-demo")//訪問的服務名如果帶有下劃線啟動會報錯
public interface SchedualServiceHello {
@RequestMapping(value = "/hello",method = RequestMethod.GET)
String sayHelloFromClientOne(@RequestParam(value = "name") String name);
}
寫一個測試Controll,通過上面定義的Feign客戶端SchedualServiceHi 來消費服務。程式碼如下:package com.example.feign.controller;
import com.example.feign.feign.SchedualServiceHello;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class FeignController {
@Autowired
SchedualServiceHello schedualServiceHello;
String port;
@RequestMapping("/hello")
public String home(@RequestParam String name) {
return schedualServiceHello.sayHelloFromClientOne(name);
}
}
3 總結
通過 Rest+Ribbon 和 Feign, 我們能把HTTP遠端呼叫對開發者完全透明,得到與呼叫本地方法一致的編碼體驗。這一點與阿里Dubbo中暴露遠端服務的方式類似,區別在於Dubbo是基於私有二進位制協議,而它們本質上還是個HTTP客戶端。如果是在用Spring Cloud Netflix搭建微服務,一般我們選擇 Feign 。